Officials found packages containing explosives at Heathrow Airport, London City Airport and the Waterloo Station train hub, Tuesday.

All three devices were sent in the same padded mail packaging, A4-sized white postal bags containing yellow Jiffy bags. All were relatively small, "capable of igniting an initially small fire." UK police have launched a terror investigation. The first package was found at The Compass Centre on Heathrow’s campus at 9:55 a.m. , about 1,000 feet from the tarmac. The building was evacuated. A second device was discovered in a post room at Waterloo around 11:40 a.m.

The third turned up inside City Aviation House at London City Airport around 12:20 p.m., prompting the evacuation of that building. Officials say train services to City Airport were suspended as a precaution but have been restored and the building where the package was found was evacuated. Flights were not affected. Only one device, the one near Heathrow, was opened. The package partially burned. Nobody was injured, and no travel disruptions resulted. No arrests have been made. At the same time, nobody has claimed responsibility for the devices. The official terrorism threat level throughout Britain is set at “severe,” indicating that intelligence analysts believe an attack is highly likely.